Our in vivo studies with E. coli rho mutants demomstrated that the lambda N gene product anti-terminates transcription at both Rho-dependent and Rho-independent termination signals. It is, however, unable to do so at certain Rho-dependent termination signals. N is, therefore, an anti-termination protein but not an antagonist of Rho. We have developed in vitro assays for the purification of N and CII gene products of lambda using a coupled transcription-translation system and lambda DNA templates in which either the gal K gene or the lac Z gene is fused to appropriate promoters, viz. pL, Pint and pre. The mechanism of action of these proteins on lambda promoters to control the integration and expression of the viral genome is being studied.